Disables stats.php for regular users to prevent usage data from falling into the wrong hands and reduces the potential attack surface of MyBB.

Disables stats.php for regular users (non-moderators) and dynamically
removes references to stats.php from the default template. Disabling
stats.php makes it more difficult to gather usage data for nefarious
purposes (e.g. a competitor) and also reduces the potential attack surface
of MyBB.